As the market for VFD (variable frequency drive) motors in the marine winch environment has matured, the need for higher rotational speed is desired. The higher rotational speeds generate substantially more kinetic energy which is then combined with the potential energy from the suspended load. During an over-speed condition, the delay in the control system will allow an increase in motor speed beyond the motor max speed, thus further increasing the kinetic energy. As the interest in such high-speed applications increases, the desirability of an enclosed spring-applied, electrically released brake capable of absorbing the higher energy increases.
Common brakes in the industry only utilize a single friction disc. Additional torque and energy capacity is obtained by increasing the diameter of the friction interfaces. Increasing the diameter of the friction interfaces also increases the centripetal force and reduces the allowable speed. Increasing the diameter and number of friction interfaces may induce instability that is detected by a vibration or whirling condition. Multi-disc brakes are typically limited to horizontal shaft applications due to increased drag of the disc pack when operating in a vertical shaft configuration.
Another necessary feature for a brake operating in a marine environment is ease of maintenance and accessibility. During commissioning and maintenance procedures, the brakes may require a provision to manually release the disc pack without using the electromagnetic release function.
Further, a major drawback to multi-disc brake designs in the past has been the friction-induced vibration/shaft whirl that often occurs during a braking event.